1. Field of the Invention
This invention relates to a novel polymer alloy coating, in particular a polymer alloy coating having enhanced adhesiveness to metal substrates which are exposed to extreme temperatures, pressures and corrosive environments encountered, for example, in oil and gas well tubulars, particularly in the pipe couplings.
2. Prior Art
In the producing of oil and gas wells it is necessary to use a large number of pipe or tubular sections connected by couplings, which are screwed to the pipe. The interior of these pipes, as well as the couplings, are often subjected to continuously high temperatures, e.g. up to about 210.degree. C., high pressures, e.g. up to about 20,000 psi, and an extremely corrosive environment produced by chemicals such as hydrocarbons, carbon dioxide and hydrogen sulfide in the presence of water. In order for a coating used on such pipes and couplings to protect the metal substrate from corrosion, the coating must be resistant to attack and maintain its adherance to the metal substrate under such conditions.
Arylene sulfide polymers are well known in the art, see U.S. Pat. No. 3,354,129 to Edmonds, Jr. et al (Phillips Petroleum Co., 1967). Generally, these polymers consist of a recurring aromatic structure coupled in repeating units through a sulphur atom. Commercially available arylene sulfide polymers which have been used for coating oil and gas well pipe couplings are polyphenylene sulfides. Polyphenylene sulfides have the general formula: ##STR1##
The polyphenylene sulfides found useful for such coatings have high melting points, outstanding chemical resistance, thermal stability and are non-flammable. These polymers are characterized by stiffness and good retention of mechanical properties at elevated temperatures as well as the ability to flow and deform smoothly, thereby prevent the galling of threads even at high thicknesses, i.e. greater than 10 mils. A highly preferred polyphenylene sulfide for such use is sold by Phillips Petroleum Company under the trademark RYTON.
The polyphenylene sulfide coatings have been found to have excellent stability under the adverse conditions found in oil and gas well production pipe. However, with the advent of fuel shortages and higher fuel prices it has become economically feasible to drill deeper wells. Along with such increased depths have come higher pressures, temperatures and corrosive environments and new type production pipe and couplings, making the known polyphenylene sulfide coatings more susceptible to permeation by water, carbonic acid, hydrogen sulfide, etc. resulting in poor adhesion, i.e., disbonding and blistering, of the coating to the metal substrate.
The Assignee in prior filed U.S. application Ser. No. 68,571 filed on Aug. 31, 1970, by Goodman (now abandoned) realized that the adhesion of polyphenylene sulfide to a metal substrate was not satisfactory under severe environmental conditions. Several theories were put forth in Goodman, i.e., lack of adequate wetting of the steel substrate by the polyphenylene sulfide, lack of polar chemical groups to contribute to the adhesion of the polyphenylene sulfide to the steel substrate, oxidation of the steel substrate to form a poor bonding surface for the polyphenylene sulfide when heated to such high temperatures of application, etc. Goodman attempted to solve this problem of poor bonding and adhesion of the polyphenylene sulfide to the metal substrate by mixing with the resin powder a small quantity of powdered tin. The powdered tin was mixed with a fluxing agent for the tin, suitable liquid carrier and a binder and then applied to a clean metal substrate. The mixture was then heated to a temperature in excess of 650.degree. F. (343.degree. C.) to melt the tin and polyphenylene sulfide resin and to drive off the liquid carrier. This type coating was found not to be as satisfactory as initially thought and the Goodman application was abandoned. This problem has remained unsolved until this invention.
There are a myriad of polyimide type resins whose properties are generally well known in the art. Exemplary U.S. Pat. Nos. describing such polyimides and their uses are: 3,179,630 to Scroog et al (1965); 3,179,631 to Scroog et al (1965); 3,179,632 to Hendrix (1965); 3,179,633 to Endrey (1965); 3,179,634 to Edwards (1965); 3,454,445 to Durst et al (1969); 3,505,277 to Soehngen (1970); 3,562,223 to Bargain (1971); 3,582,458 to Haller (1972); 3,708,458 to Alberino et al (1973); 4,054,704 to Vassiliou (1977); 4,054,705 to Vassiliou (1977); and 4,064,303 to Vassiliou (1977);
These polyimide resins are known to be useful as shaped structures, self-supporting films, fibers, filaments and coatings. They, generally, have high tensile strength, are infusible, insoluble, stable to heat, water and to corrosive environments. The films may be used in corrosion resistant pipe, pipe-lagging and duct work, for containers and container linings and in laminating structures where the films are bonded to the sheet metal or foils, oven interiors, and electrical insulation.
Particularly unique polyimides are derived from the homopolymerization or polymerization of acetylene terminated aromatic polyimide oligomers. These polyimides and their preparation are described in Landis et al, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., Vol. 15, No. 2, Jan. 9, 1974, pp 537-41; U.S. Pat. Nos. 3,845,018 (1974), 3,864,309 (1975) and 3,879,349 (1975) all to Bilow et al; and U.S. Pat. No. 4,307,220 to Lucarelli et al (1981). These addition curable polyimide oligomers crosslink and cure without offgassing to produce low void moldings and structural composites of high strength which are stable up to 370.degree. C. Some of these polyimide oligomers are sold by Gulf under the trademark THERMID. The properties of some of these polyimides are described in Gulf Advanced Materials, "Formulating Adhesives with THERMID 600" (undated) and various technical bulletins from Gulf which are incorporated herein by reference and made a part of this file (28 pages).
There are numerous references which describe blends or laminates of polyphenylene sulfide or polyimides. The aforementioned Edmonds, Jr. et al indicates that polyphenylene sulfide may be blended with fillers, pigments, stabilizers, softeners, extenders and other polymers. No specific examples are given of such polymer blends. The coating of pipes to prevent corrosion resistance is also described.
Phillips Petroleum company, Research and Development Report 5701-70 Rev., Unit No. 798, Feature No. 7101, July 1, 1970 states that polyphenylene sulfide has a strong affinity for a variety of fillers and that thermally stable materials have been used to modify color, gloss, coefficient of friction and flexibility, making polyphenylene sulfide useful for both protective coatings and non-stick coatings.
Phillips Petroleum Company, Research and Development Report 5832-70 Rev., Unit No. 798 Feature No. 7101, Jan. 6, 1971, describes polyphenylene sulfide coatings applied to steel and aluminum substrates by dry powder spraying. The report states that " . . . addition of fillers was found to be desirable to improve adhesion, appearance, and color, and addition of PTFE (polytetrafluorethylene) produced `non-stick` coatings". The only other fillers described are TiO.sub.2 and Fe.sub.2 O.sub.3.
Phillips' Technical Service Memorandum-275, July, 1976 describes using polyphenylene in high temperature and corrosive environments, such as pipe couplings, pumps, valves, tanks, reactors, sucker rods, oil well tubing and fan drive discs. The memorandum further states that polyphenylene sulfide has an excellent affinity for a variety of fillers which can withstand the 700.degree. F. (371.degree. C.) curing temperatures. The only blend suggested in the memorandum is polyphenylene sulfide with PTFE. PTFE composities with polyphenylene sulfide are also described in Arkles et al "Wear Behaviour of Thermoplastic Polymer-Filled PTFE Composites" Journal of the American Society of Lubrication Engineers, Vol. 33, 1, 33-38, January, 1977.
U.S. Pat. No. 3,744,530 to Perry (Phillips Petroleum Co., 1973) describes polyphenylene sulfide coated pipes and methods of coating such pipes. The polyphenylene sulfide coating used contains a filler, such as iron oxide, in an amount of between about 5% to about 30% by weight.
U.S. Pat. No. 3,801,379 to Blackwell (Phillips Petroleum Co., 1974) describes treating an aluminum surface with water at a temperature of at least 70.degree. C. to enhance the adherance of arylene sulfide polymer thereto. This is said to be an improvement over primers for the substrate or incorporating additives into the polymer to improve adhesion.
U.S. Pat. No. 3,819,407 to Oates et al (1974) describes a high temperature and erosion resistant laminate comprising a polyimide layer coated with a poly(arylene sulfide) resin.
U.S. Pat. No. 4,017,555 to Alvarez (1977) is directed to polymeric alloys of polyphenylene sulfide and polyimides used for molding structures. The polyimides used in Alvarez do not melt and must be fabricated by machining, punching or by direct forming techniques. The preferred polyimide resin molding powder is a completely imidized, fully reacted aromatic polyimide resin of the type described in the aforementioned U.S. Pat. No. 3,708,458 to Alberino et al (1973) and sold under the trademark POLYIMIDE 2080 by the Upjohn Company. Alvarez (and also Alvarez et al, "High Temperature Performance Polymeric Alloys", Society of Plastics Engineers, Tech. Paper 35-308, 1977), indicates that the optimum ratio of polyphenylene sulfide to polyimide is 50/50 to 80/20, i.e. alloys containing less than 20% polyimide are undesirable.
U.S. Pat. No. 4,156,049 to Hodes et al (1979) describes a laminate for antifriction and slide members. The laminate comprises a metallic substrate strip having bonded to a surface a slide layer of thermosetting polyimide resins, and additives which improve the running properties of a bearing, such as polytetrafluorethylene. The slide layer additionally can contain polyimide resins and other additives, in fine grain or fine powdered form. The fine grain or fine powdered polyimide resin mixture, may be supplemented with a highly heat and abrasion resistant thermoplastic, preferably polyphenylene sulfide.
U.S. Pat. No. 4,139,576 to Yoshimura et al (1979) describes a fluorocarbon polymer coating composition which includes a polyarylene sulfide resin, e.g. polyphenylene sulfide and at least one imido containing resin e.g. polyimide. The fluorocarbon polymer is a necessary element of Yoshimura et al.
Other references of interest are:
NASA Tech Briefs, Spring 1981 "Elastomer-Toughened Polyimide Adhesives", describes the use of addition polyimides as high-temperature adhesives for bonding composite materials and such metals as titanium. The incorporation of elastomers, e.g. fluorosilicone rubber, SYLGARD 184 resin from Dow Corning, an aromatic amine-terminated butadiene/acrylonitrile, and an aromatic amine-terminated silicone, into the polyimide matrix was used to modify polymer toughness. All four additives increased the peel strength of the polyimides.
U.S. Pat. No. 3,652,409 to Mack et al (1972), describes a composition containing polytetrafluoroethylene resin and polyimide resin to produce a molded shape having exceptional resistance to frictional wear.
U.S. Pat. No. 3,658,938 to Kwitkowski et al (1972) describes a mechanical blending of polysulfones with certain polyamide/imides where shaped articles and the like are to be fabricated by injection molding techniques.
U.S. Pat. No. 3,712,932 to Balme (1973) describes a film forming heat stable composition comprising a polysulfone and a specific type imide pre-polymer. The compositions are said to be suitable for the preparation of films and fibers and for the preparation of coatings, adhesives and laminated materials.